1. Field of Invention
This invention relates to the art of injection molding of resinous materials and, more particularly, to the opening and closing of an injection nozzle to achieve improved operation and control of the flow of plasticized material through the nozzle.
2. Description of Prior Art
In the manufacturing process of plastic parts a positive shut-off of the nozzle is very important to avoid drool from the nozzle into the mold cavity while the mold halves have been separated while the part is being removed. It is obvious that if the nozzle drools into the mold, the resin will partially solidify and upon the next injection molding step, the partially solidified resin will cause an anomaly in the part manufactured. Also hydraulic cylinders are used to actuate the nozzle rod with the attendant problems of hydraulic fluid leakage and high maintenance.
One type of nozzle shut-off is shown in U.S. Pat. No. 2,318,031 issued to Tucker. Here, the nozzle utilizes a rotary valve mounted at the output of the nozzle itself. This valve in turn is rotated by a hydraulic motor which disconnects a passage through the valve body to disconnect the flow of plasticized resin. Another valving method is shown in this patent wherein the opening of the nozzle is accomplished by a pure mechanical means. Here a valve closure has a rod connected to the valve protruding from the end of the nozzle. As the mold is closed, the rod engages the mold surface and opens the valve to allow material to flow into the mold. As the mold is opened the valve will shut off from the pressure of the resin inside the unit.
U.S. Pat. No. 3,231,938 issued to Seymour shows a spring operated nozzle means wherein the flow of plasticized resin will increase the pressure in the nozzle and cause the shut-off to be pushed against the spring, thus opening the entrance to the mold. Upon completion of the injection step, the pressure of the resin will be reduced and the spring will push the shut-off member back into its original position thereby disconnecting the flow of plasticized resin to the mold. Another U.S. Pat. No. 3,241,191 issued to Nouel shows a spring-lever type mechanical method for operating the shut-off valve whereby resin under pressure forces the nozzle shut-off to a mid-position acting to regulate the flow of resin through the tip of the nozzle. The valve is double acting and when the mold is filled the pressure of the resin inside the mold will force back the shut-off through a mechanical arm against a spring which shuts off the flow of resin to the mold. Here the flow of resin and spring biasing means are used to open and return the valve to its shut-off position.
U.S. Pat. No. 3,571,856 issued to Voelker shows a shut-off means whereby the control is by a hydraulic actuator which is connected to a rod inside a ball and socket connected to a manifold means having an orifice opening into the mold. The rod is capable of being moved to open or shut off the orifice to the mold. The rod operates as a valve to disconnect plasticized resin from flowing through the nozzle means through the orifice into the mold cavity.
Another means of shutting off or disconnecting the flow of plasticized resin through a nozzle is shown in U.S. Pat. No. 3,902,665 issued to Hendry, the instant inventor. This patent shows various nozzle shut-off means being operated by a fluid pressure to stop the flow of plasticized resin from the extruder into the nozzle itself. Here, the opening and closing of the nozzle shut-off means can be by a fluid means or the opening of the shut-off can be caused by the force of plasticized resin against the shut-off rod pushing the valve back to its seated position. The return to a closed position is by a compressed air or fluid means. U.S. Pat. No. 3,649,148 issued to Waltman shows a means for controlling the orifice of a nozzle which operates using a fluid means to control the wall thickness of plasticized resin as it is extruded from the nozzle in the manufacture of blow molded bottles.
My invention improves on the prior art by accurately controlling the flow of plasticized resin through the nozzle. This is accomplished by a control rod means which interacts with the shut-off plunger means. This control rod controls the length of movement of the shut-off plunger by controlling the distance or length of movement of the plunger which in turn controls the volumetric opening. The amount of plasticized resin that can flow through the nozzle and the nozzle tip is therefore accurately controlled. An adjusting means allows more or less resin to flow through the nozzle tip by adjusting the position of the control rod with respect to the plunger and its position relative to the volumetric flow. Through the center of the control rod is a bore which allows the input of fluid pressure to shut off the nozzle after the correct amount of resin has been injected into the mold. This method of shut-off utilizes either compressed air, nitrogen or some other fluid medium for forcing the plunger into the tip of the nozzle thereby discontinuing the flow of the plasticed resin.
In summary, my invention consists of an injection molding nozzle means having a slideable shut-off plunger which is accurately positioned on and interacts with a control rod means for controlling the volumetric flow of resin. The control rod passes through the center of the nozzle body and has a bore down the center of the control rod which exits into a chamber formed in the shut-off plunger. When the resin flow is first initiated this chamber is vented to atmosphere or to some low pressure, thereby allowing the pressure of the plasticized resin acting on a differential area to move the plunger to open the nozzle. The plunger will move until it bares against the end of the control rod and cannot move any additional distance. Upon completion of the cycle, the pressurization of this chamber allows the plunger to move forward shutting off the flow of plasticized resin.
It is an object of this invention to have the control rod adjustable by threaded means to control the length of movement of the plunger. Another object of the invention is to have the end of the plunger means flush with the end of the nozzle tip upon shut-off of the nozzle. It is an object of this invention to have guide pin means mounted to the control rod for spacing the rod internal to the nozzle body. It is the object of this invention to manufacture the nozzle so that it is directly mountable to a manifold member. It is an object of this invention to control the volumetric opening of the nozzle to acurately meter the flow of plasticized resin. It is the object of this invention to use a non-hydraulic means to operate the nozzle.